There isn’t a plugin that I know of. How many comments are we talking about? I’m assuming to many to manually approve.
A simple solution I can think of would be adding something like this to the comment loop in comments.php. Find the foreach loop and replace it with something like
<?php
//set the date one day into the future
$date = strtotime(date("Y-m-d", strtotime($date)) . " +1 day");
foreach($comments as $comment) :
if($date > comments->comment_date ){
<?php comment_text(); ?>
<cite><?php comment_type(); ?> by <?php comment_author_link(); ?> on <?php comment_date(); ?> at <?php comment_time(); ?></cite> }
endforeach;
?>
This is untested and just an example. You should be able to set $date to whatever you want or even use a random time.
Resources:
get_comments()
Unraveling the Secrets of WordPress’ Comments.php File
PHP Date add 1 hour